1. Field of the Invention
The present invention relates to a compound semiconductor light emitting diode, and more particularly, to a light emitting diode which may be connected to an alternating current (AC) power source.
2. Discussion of the Background
Compound semiconductor light emitting diodes (LEDs), e.g., GaN-based LEDs are widely used for display elements and backlights. Further, these LEDs may consume less electric power and have a longer lifespan compared with conventional light bulbs or fluorescent lamps. Therefore, their application areas have been expanded for general illumination while substituting for conventional incandescent bulbs and fluorescent lamps.
An LED is repeatedly turned on/off depending on a direction of current when operating under AC power. Therefore, when the LED is directly connected to an AC power source, the LED may not continuously emit light and may be easily damaged due to reverse current.
An LED capable of being directly connected to a high-voltage AC power source is disclosed in PCT Patent Publication No. WO 2004/023568A1 (SAKAI et al.), entitled “LIGHT-EMITTING DEVICE HAVING LIGHT-EMITTING ELEMENTS”. Further, LEDs having various structures have been developed.
According to PCT Patent Publication No. WO 2004/023568A1, light emitting elements (hereinafter, “light emitting cells”) are two-dimensionally connected in series on a single insulating substrate, such as a sapphire substrate, to form light emitting cell arrays. Two light emitting cell arrays are connected to each other in reverse parallel on the substrate, so that light is continuously emitted by an AC power supply.
In PCT Patent Publication No. WO 2004/023568A1, one of the light emitting cell arrays operates during one half period of AC power, and the other array operates during the other half of the AC power. That is, half of the light emitting cells in an LED operate until a phase of the AC power is changed. Therefore, the use efficiency of the light emitting cells does not exceed 50%.
Meanwhile, Korean Patent Laid-Open Publication No. 10-2006-1800 discloses an LED, in which a bridge rectifier is formed on a substrate using light emitting cells, and an array of light emitting cells connected in series is disposed between two nodes of the bridge rectifier, so that the LED operates under AC power. Accordingly, the array of light emitting cells connected in the bridge rectifier emits light during both phases of AC power (i.e., full-wave light) regardless of changes in phase of AC power, so that the use efficiency of light emitting cells may be increased.
However, as the number of light emitting cells connected in the bridge rectifier increases, a high reverse voltage may be applied to a specific light emitting cell in the bridge rectifier, and therefore, the light emitting cell in the bridge rectifier may be damaged. As a result, the LED may be damaged. Therefore, the number of light emitting cells in the array of light emitting cells connected in the bridge rectifier may be decreased. However, when the number of light emitting cells is decreased, it may be difficult to provide an LED capable of operating under high-voltage AC power. The reverse voltage may alternatively be decreased by increasing the number of light emitting cells connected in the bridge rectifier. However, the use efficiency of light emitting cells may accordingly be lowered.
Meanwhile, efforts have been continuously made for enhancing light emission output per a chip area of a high-voltage AC LED and improving its reliability. Particularly, an LED is being developed in which a plurality of light emitting cells are arranged on a chip having a square flat contour and in which the light emitting cells are effectively and safely connected to each other using wires.